![](http://datasheet.mmic.net.cn/330000/PM4354-PI_datasheet_16444274/PM4354-PI_399.png)
RELEASED
PM4354 COMET-QUAD
DATASHEET
PMC-1990315
ISSUE 6
FOUR CHANNEL COMBINED E1/T1/J1
TRANSCEIVER / FRAMER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC. AND FOR ITS CUSTOMERS’ INTERNAL USE
384
alignment of RX-ELST. The transmit frame alignment is either arbitrary (when the TX-ELST is
used) or is specified by the BTFP[x] input (when the TX-ELST is bypassed). Conceptually, the
data flow through a single quadrant of the COMET-QUAD in this loopback mode is illustrated in
Figure 34. Note that because the transmit and receive streams are not superframe aligned, any
robbed-bit signaling in the receive stream will not fall in the correct frame once looped back and
that transmit robbed-bit signaling will overwrite the looped back data if signaling insertion is
enabled.
Figure 34:
- Payload Loopback
BTIF
BRIF
TX
ELST
RX
ELST
Transmitter
T1-XBAS /
E1-TRAN
Framer
T1-FRMR /
E1-FRMR
TJAT
RJAT
CDRC
XLPG
RLPS
TXTIP[x]
TXRING[x]
RXTIP[x]
RXRING[x]
Payload Loopback
BTPCM[x]
BTSIG[x]
BTCLK[x]
BRPCM[x]
BRSIG[x]
BRCLK[x]
12.11.3 Per-Channel Loopback
The T1 or E1 payload may be looped back on a per-channel or per-timeslot basis through the use
of the TPSC. If all channels are looped back, the result is very similar to Payload Loopback. In
order for per-channel loopback to operated correctly, the receive elastic store, RX-ELST, must be
bypassed by setting the RXELSTBYP bit to logic 1 and the backplane receive interface must be
set to clock master by setting the CMODE bit in the BRIF Receive Backplane Configuration
register to logic 0. The LOOP bit must be set to logic 1 in the TPSC Internal Registers for each
channel/timeslot desired to be looped back, and the PCCE bit in the TPSC Configuration register
must be set to logic 1. When all these parameters are configured, the incoming receive
channels/timeslots selected will overwrite their corresponding outgoing transmit
channels/timeslots; the remaining transmit channels will pass through intact. Note that because
the transmit and receive streams are not superframe aligned, any robbed-bit signaling in the
receive stream will not fall in the correct frame once looped back and that transmit robbed-bit
signaling will overwrite the looped back channel data if signaling insertion is enabled.